1. Matthew Casali and Robert Fahey
Mapping temporal change in oak-dominated ecosystems in the Chicago metropolitan region
Matthew Casali and Robert Fahey
Forest Ecology Laboratory, Department of Research, The Morton Arboretum, Lisle, IL
Oaks are a keystone species in Northeastern Illinois, driving much of the biodiversity in the region. In this region and across eastern North America oak ecosystems are in decline due to landscape-level changes such as alteration of disturbance regimes, habitat fragmentation, and urban development (Abrams 2003, Fahey et al. 2013). In addition, stand-level changes such as competition from shade- tolerant species, encroachment of invasive plant species, and lack of management or disturbance- related canopy openings have lead to widespread oak reproductive failures (Lorimer 1994, Nowacki and Abrams 2008). The goal of this project was to identify existing oak-dominated communities throughout the seven Northeastern Illinois counties of the Chicago metropolitan region (Cook, DuPage, Kane, Kendall, Lake, McHenry, and Will). The current distribution of oak-dominated ecosystems was compared spatially and temporally with records from multiple time periods dating back to the 1800s (McBride and Bowles 2007).The project provides spatially explicit information regarding the quantity and parcel size of remaining oak ecosystems, their ownership and conservation status, and relationship to drivers of change from original distribution.
Introduction
Results
Discussion and Continuing Research
Our findings indicate a significant decline in the extent of oak ecosystems from pre-settlement baselines across the region, but also high spatial variability in this landscape transition and its drivers.
Estimated area of oak-dominated ecosystems declined from 782,709 acres in the 1830’s to 209,951 acres in 1939 (27% remaining), and 111,518 in 2010 (14%).
The highest percentages of oak ecosystems retained in 2010 (relative to pre-settlement conditions) were found in exurban Kendall County (27%) and highly urbanized Cook County (19%)
The lowest percentages of oak ecosystems retained were found in exurban McHenry County (10%) where oak ecosystems were especially dominant in the pre-settlement landscape.
Conservation status also differed greatly across the region; the highest percentage of protected ecosystems was found in Cook County (82%) and the lowest in Kendall County (14%).
Our findings illustrate the high degree of oak ecosystem loss and variable spatial patterns of that loss across the Chicago metropolitan region. Further data analysis from this project will illustrate the effects of patterns of urban development on landscape composition. These data will be essential in regional oak conservation efforts – including illustrating the importance of private lands and identifying high priority areas for acquisition or restoration that could create connections between existing large parcels.
Table 1. Areal extent of oak ecosystems in each time period and proportion of modern ecosystems with protected status based on Green Infrastructure Maps (CMAP 2012)
Oak ecosystem acreage
Percentage remaining
County
1830s
1939
2010
Protected (acres)
% Protected
Cook
119,100
34,571
22,358
29%
19%
18,369
82%
DuPage
39,219
15,509
6,995
40%
18%
4,009
57%
Kane
126,764
25,893
14,278
20%
11%
3,742
26%
Kendall
27,516
10,879
7,440
27%
1,073
14%
Lake
187,234
48,456
24,003
13%
8,494
35%
McHenry
182,459
26,612
18,003
15%
10%
3,182
Will
100,417
30,028
18,441
30%
8,109
44%
Total
782,709
191,948
111,518
25%
46,978
42%
Figure 1. Spatial distribution of oak ecosystems in 1939 and 2010 – background shading illustrates ecosystems mapped in original landscape based on PLS notes (McBride and Bowles 2007) - green indicates forested areas.
Methods
Oak-dominated ecosystems were identified from pre-European settlement data,1939 aerial photography, modern soils data, and orthoimagery from 2010 and mapped using ArcGIS. The pre-European settlement data was a product of seven reports ranging from 1998 to 2005 by the Plant Conservation Lab at the Morton Arboretum (McBride and Bowles 2007). Using the 1939 aerial imagery, oak-dominated parcels were located and digitized. Probable oak dominance for each parcel was evaluated based on species data from public land survey notes, landscape position, soil data, and user interpretation of the imagery based on tone, shape, size, texture, and association. These parcels are then compared to the 2010 orthoimagery and are reshaped or removed to include only the previously existing oak communities.
Figure 3. Locations of 2010 oak ecosystem parcels by protected status (CMAP 2012).
Literature cited
Abrams, M. D Where has all the white oak gone? BioScience 53:
Chicago Metropolitan Agency for Planning (CMAP) Refinement of the Chicago Wilderness Green Infrastructure Vision Final Report. space/green-infrastructure-vision
Fahey, R.T., M. Bowles, and J. McBride Origins of the Chicago urban forest: composition and structure in relation to pre-settlement vegetation and modern land-use. Arboriculture and Urban Forestry 38 (5)
Lorimer, C. G Causes of the oak regeneration problem. Pages Oak Regeneration: Serious Problems, Practical Recommendations, USDA Forest Service General Technical Report SE- 84, Southeastern Forest Experiment Station, Asheville, NC.
McBride, J. & Bowles, M Pre-European Settlement Vegetation of the Chicago Region. Interactive Maps and Reports. The Morton Arboretum, Lisle, Ill.
Nowacki, G. J. and M. D. Abrams The demise of fire and “mesophication” of forests in the eastern United States. BioScience 58:
Acknowledgements
Funding for this project was provided by USDA Forest Service State and Private Forestry, The Morton Arboretum and Chicago Wilderness. Assistance was provided by Jim Anderson, Chris Mulvaney and participants in the CW Oak Recovery Working Group.
Figure 2. Spatial distribution of oak ecosystem parcels ≥100 acres in area in 1939 and 2010.